Field
The present disclosure relates generally to compound semiconductor devices, and more specifically, to a heterojunction bipolar transistor unit cell and power stage for a power amplifier.
Background
A wireless device (e.g., a cellular phone or a smartphone) in a wireless communication system may include a radio frequency (RF) transceiver to transmit and receive data for two-way communication. A mobile RF transceiver may include a transmit section for data transmission and a receive section for data reception. For data transmission, the transmit section may modulate a RF carrier signal with data to obtain a modulated RF signal, amplify the modulated RF signal to obtain an amplified RF signal having the proper output power level, and transmit the amplified RF signal via an antenna to a base station. For data reception, the receive section may obtain a received RF signal via the antenna and may amplify and process the received RF signal to recover data sent by the base station.
The transmit section of the mobile RF transceiver may amplify and transmit a communication signal. The transmit section may include one or more circuits for amplifying and transmitting the communication signal. The amplifier circuits may include one or more amplifier stages that may have one or more driver stages and one or more power amplifier stages. Each of the amplifier stages includes one or more transistors configured in various ways to amplify the communication signal. The transistors configured to amplify the communication signal are generally selected to operate at substantially higher frequencies for supporting communication enhancements, such as carrier aggregation. These transistors are commonly implemented using compound semiconductor transistors, such as bipolar junction transistors (BJTs), heterojunction bipolar transistors (HBTs), and the like.
The implementation of carrier aggregation in mobile RF transceivers enables a wireless carrier to maximize available bandwidth by simultaneously using multiple frequencies for a single communication stream. While an increased amount of data is provided to the end user, successful implementation of carrier aggregation complicates thermal power specification of power amplifiers in the mobile RF transceiver. These thermal power specifications are further complicated because RF power amplifiers are generally not fabricated using a CMOS (complementary metal-oxide-semiconductor) process. Rather RF power amplifiers are often fabricated using column III and column V (III-V) or column II and column IV (II-VI) compound semiconductor materials that generally exhibit poor thermal conduction capabilities. Consequently, it is difficult to meet thermal power specifications in III-V or II-VI compound semiconductor devices, such as heterojunction bipolar transistor (HBT)-based power amplifiers.